Some people who drink water containing TTHM above the MCL over many years may experience problems with their liver, kidneys, or central nervous system and may have an increased risk of developing certain types of cancer. Those with a severely compromised immune system, caring for an infant, pregnant, or elderly may be at increased risk.
Cancer risks generally accrue over lifetimes and very long periods of exposure. For disinfectant byproducts like TTHM, risks are typically calculated with a daily average of drinking 2 liters of water over a lifetime of 70 years. Research on the connections between Total THM exposures and these health risks is underway.
Water that meets the total THMs guideline is considered safe for all domestic uses, including drinking, bathing, showering, and food preparation. The risk of illness from TTHM is much lower than that of drinking water that has not undergone disinfection.